A boy in the city of Homs holds the remains of a mortar, following shelling of the city. Photograph: Reuters

The Syrian military took its bombardment of the Baba Amr district of Homs into a fourth week on Saturday as the Red Cross tried to evacuate more traumatised civilians.

At least 28 people were killed , nine of them in Homs, according to the Syrian Observatory for Human Rights. Thousands are trapped in the Baba Amr suburb.

Deploring the outcome of the international "Friends of Syria" conference in Tunisia on Friday, opposition activists and civilians in Homs said that they felt forgotten. People talked of how the world had abandoned them to be killed by the soldiers and rockets of President Bashar al-Assad.

After its ambulances had been allowed to leave the city with 27 people on Friday, the International Committee of the Red Cross (ICRC) said that it had resumed negotiations with both sides to enable more civilians to be brought out. There was still no sign of progress on the evacuation of the western journalists injured in the rocket attack that killed reporter Marie Colvin, 56, and the French photographer Rémi Ochlik, 28, on Wednesday.

The Sunday Times photographer Paul Conroy, who has shrapnel wounds in his legs, and the French reporter Edith Bouvier, who has a broken leg, remain in Homs, as do two other western journalists, Javier Espinoza, from the Spanish newspaper El Mundo, and a French freelance reporter, William Daniels, who are unhurt. Efforts are continuing to get them out, along with the bodies of their colleagues. The Sunday Times today revealed that Colvin died trying to retrieve her shoes so she could escape the bombardment. The journalists had followed the Middle Eastern custom of taking off their shoes when they went into a building housing a rebel press centre, and tried to recover them as rockets fell.

Colvin was on the ground floor when missiles hit the upper floors. The journalists were covered in dust but unhurt. They prepared to flee but had to get their shoes first. Colvin ran to the hall, where she had left hers, but when she got there a rocket landed at the front of the building, a few yards away. The blast killed her and Ochlik.

The newspaper said hopes had faded for the rescue of Conroy and Bouvier, who both urgently need medical treatment, and the others.

Reports said the evacuation had run into trouble because of distrust between the two sides during a ceasefire.

Conroy was reported to be refusing to leave without Colvin's body despite being in danger of potentially life-threatening infection if his wounds were not treated.

People in Homs – a city of more than 800,000 at the crossroads of highways from Damascus to Aleppo and from the coast to the interior – are suspicious of evacuations, carried out by the ICRC's local partner, the Syrian Red Crescent.

A UK-based activist, Abdul Omar, told the BBC that people did not want to get into the ambulances. "We know that the Syrian regime has in the past used Red Crescent ambulances to pretend that they are rescue operations but they have ended up arresting individuals, arresting civilians and taking them to prison," he said.

But the ICRC denied there was anything but a mercy mission under way with the Red Crescent vehicles, and said that there was no difference between the two groups. "Their volunteers are risking their lives on a daily basis to help everyone with no exceptions," ICRC spokesman Hicham Hassan said in Geneva.

The Tunis conference of western, Arab and other countries was intended to increase diplomatic pressure on Assad to end an 11-month crackdown on opponents of his rule.

The US secretary of state, Hillary Clinton, said Assad would be held to account for the bloodshed and sharply criticised Russia and China, which have blocked UN measures against Syria.

But to beleaguered Syrians the speeches seemed remote. "The people resent what happened in Tunis," said a doctor in the restive town of Zabadani. "We need them to arm the revolution. I don't understand what they are waiting for. Do they need to see half the people of Syria finished off first?"

Diplomacy is hamstrung because Russia and China oppose action by the UN security council, and there is little appetite for military intervention – although Saudi Arabia has suggested it might arm the rebels, a move that prompted an angry reaction from Damascus, which accused the Saudis of being "partners" in the bloodshed in Syria.

Despite international condemnation of his rule, Assad is due to stage a referendum today on a new constitution that he says will lead to a multiparty parliamentary election within three months. The opposition has called for a boycott of the vote, deriding his reform pledges and demanding again that he step down. Turkey's foreign minister, Ahmet Davutoglu, also questioned how the vote could take place.

"On one hand you say you are holding a referendum and on the other you are attacking with tank fire on civilian areas. You still think the people will go to a referendum the next day ?" he asked.